I just don't understand how anal sex is physically possible, especially when it comes to oversized penises or toys. Don't get me wrong, I understand that it's all quite possible, somewhow. But what exactly happens when an 8" or 9" or 12" object is inserted into one's 5" rectum? Where does it go?

To better illustrate my confusion, here's an image of the rectum taken from wikipedia (rectum is colored red)...


The rectum is tiny! From what I read, an average of 5 inches long, at which point it makes a downward hairpin turn into the sigmoid colon. And yet every description of anal sex I can find explains that everything happens in the rectum. And every explanation of proper douching I can find, explains that only the rectum needs cleansing.

So how in god's name are people shoving 10", semi-rigid dildos into their bums?? The only way this is possible is that the inserted parts/objects are venturing into people's intestines. But how? Is the sigmoid colon just flopping around inside of us, un-anchored, able to straighten out when needed? (not to mention stretch to accommodate girthy objects). Does it then return to its original hairpin-turn shape and to its original diameter? Is this rearranging/stretching of the colon dangerous?

On a similar note: when one uses an anal douche, is the goal to clean out only the 5 inches of rectum? That's great for all those 5 inch penises out there, but does that mean there is more "stuff" lurking in that downward hairpin turn, waiting to be encountered by the 8" penis or the 10" toys? Should I be trying to irrigate the rectum and a good portion of the sigmoid colon??

This all makes no sense to me. Does anybody have any idea what's actually happening in this mysterious and seemingly magical tunnel in which the laws of physics and biology don't seem to apply?

Any help understanding this would be much appreciated.